nimsuggest: fix tcp socket leak for epc backend (#12384) [backport]

Same as e9fa4c9b9c, but for the epc
backend which is used by emacs and vscode plugin.

Since the EPC backend only deal with one connection per nimsuggest
instance, only one socket is leaked, thus not as servere as with the tcp
backend.

(cherry picked from commit edb24b7ce0)

nimsuggest/nimsuggest.nim

@@ -353,7 +353,7 @@ proc replEpc(x: ThreadParams) {.thread.} =
   echo port
   stdout.flushFile()
 
-  var client = newSocket()
+  var client: Socket
   # Wait for connection
   accept(server, client)
   while true: